A neurobiological explanation (dopamine hypothesis)

Question 1

what is a neurobiological explanation to schizophrenia?

Answer 1

The dopamine hypothesis

Question 2

what’s the term for excess dopamine?

Answer 2

Hyperdopaminergia

Question 3

Hyperdopaminergia AO1

Answer 3

Antipsychotic drugs chlorpromazine and haloperidol help symptoms of schizophrenia - but also induce side effects of tremors and muscle rigidity.
These are symptoms of Parkinson’s disease (low dopamine) - so schizophrenia was linked to high dopamine (hyperdopaminergia).

Question 4

what two antipsychotic drugs help symptoms of schizophrenia?

Answer 4

chlorpromazine and reserpine

Question 5

what are two explanation of why hyperdopaminergia may occur?

Answer 5

-Low levels of beta hydroxylase (enzyme that breaks down dopamine) may build up excess opine in synapses.

-Proliferation (rapid increase) of D2 dopamine receptors on postsynaptic cells due to hypersensitivity of a neurotransmitter may be responsible for hyperdopaminergic activity.

Question 6

What’s the term for a dopamine deficiency?

Answer 6

hypodopaminergia

Question 7

Hypodopaminergia AO1

Answer 7

-positive symptoms of schizophrenia (e.g delusions and hallucinations) may result from excess dopaminergic activity in the mesolimbic pathway.

-negative symptoms (e.g disorganised thought) may result from hypodopaminergia, a lack of dopaminergic activity in the mesocortiyal pathway.

Question 8

Excess of dopaminergic activity in what pathway results in positive symptoms?

Answer 8

Mesolimbic

Question 9

lack of dopaminergic activity in what pathway results in negative symptoms?

Answer 9

mesocortical

Question 10

Serotonin and negative symptoms
(what does clozapine bind to and how may this lead to symptoms?)

Answer 10

later research focused on the roles of other neurotransmitters (GABA, glutamate and serotonin).

Newer antipsychotic drug (clozapine) binds to D1 and D4 dopamine receptors.
The effectiveness of this drug called into question the original dopamine hypothesis (with its focus on D2 receptors).

Clozapine also binds to serotonin receptors and reduces positive and negative symptoms of schizophrenia - so negative symptoms may be caused by irregular serotonergic activity.
research then focused on the interactions between different neurotransmitters (e.g serotonin regulates dopamine levels in the mesolimbic pathway).

Question 11

Dopamine dysregulation

Answer 11

How’s and Kapur’s (2009) version of the hypothesis:

-dopamine dysregulation in the Striatum is the common pathway to psychosis (schizophrenia)

-attention should turn to high presynaptic dopamine levels as opposed to irregularities of D2 receptors.

-focus on interactions between genetic, environmental and sociocultural factors.

-Dopamine hypothesis should be softened and viewed as an explanation for ‘psychosis proneness’, not as an explanation specifically for schizophrenia.

Question 12

who conducted research into a more recent version of the dopamine hypothesis suggesting dopamine dysregulation?

Answer 12

Howes and Kapur (2009)

Question 13

what does Howes and kapur believe the dopamine hypothesis should be viewed and what do they focus on?

Answer 13

Dopamine hypothesis should be softened and viewed as an explanation for ‘psychosis proneness’, not as an explanation specifically for schizophrenia.
focus on interactions between genetic, environmental and sociocultural factors.

Question 14

strengths

Answer 14

support from amphetamine-induced psychosis in rats
Tenn et al. (2003) found that rats given nine amphetamine injections over three weeks showed various schizophrenia-like symptoms.
Dopamine antagonists (drugs that block D1 receptors) successfully reversed these effects.
This experimental evidence suggests that increased dopamine levels may be a cause of schizophrenia in symptoms.

Support for the role of D2 receptors.
Snyder (1985) found that chlorpromazine is an antagonist at many dopamine receptors (D1 and D2) and has an antipsychotic effect.
He also found that the dopamine antagonist haloperidol is more effective even though is has a narrower range of biochemical effects.
This finding suggests that excess activity at specific (but not all) dopamine receptors is implicated in development of symptoms.

Question 15

Name two supporting researchers

Answer 15

Tenn et al. 2003
Snyder 1985

Question 16

What did Tenn et al 2003 find?

Answer 16

found that rats given nine amphetamine injections over three weeks showed various schizophrenia-like symptoms.

Question 17

What did Snyder 1985 find?

Answer 17

found that chlorpromazine is an antagonist at many dopamine receptors (D1 and D2) and has an antipsychotic effect.

Question 18

state a composing argument.

Answer 18

However, Dépatie and Lal 2001 showed that apomorphine (dopamine agonist which stimulates D2 receptors) does not induce psychotic symptoms in non-psychotic clients and does not worsen symptoms in this already diagnosed. This challenges the suggestion that hyperdopaminergia is responsible for positive symptoms.

Question 19

name two researchers who challenge this hypothesis?

Answer 19

Dépatie and Lal 2001
Veling et al. 2008

Question 20

whit did Dépatie and Lala 2001 show?

Answer 20

showed that apomorphine (dopamine agonist which stimulates D2 receptors) does not induce psychotic symptoms in non-psychotic clients and does not worsen symptoms in this already diagnosed.

Question 21

weakness

Answer 21

evidence of schizophrenia in second-generation immigrants.
Neurochemical theories cannot explain why certain groups (e.g. second-generation immigrants) are more likely to be diagnosed with schizophrenia.
Veling et al. 2008 showed that moroccan immigrants were more likely to be diagnosed than Turkish immigrants (likelihood correlated with the discrimmination faced by each group).
This suggests that environmental factors (social stress) may interact with internal neurochemistry making some people more prone to psychosis because of both factors.

Question 22

application

Answer 22

research into neurotransmitters has led to drug treatments.
research shows that dopamine antagonists binding to D2 receptors (e.g haloperidol and spiroperidol) can successfully reduce positive symptoms.
Also, atypical drugs (e.g clozapine) which block serotonin receptors have been successful in treating both positive and negative symptoms.
This means that people with schizophrenia can live in the community without need of residential care because their symptoms are controlled.

Question 23

Overall what does this research lead to in the wider community?

Answer 23

led to drug treatments
meaning that people with schizophrenia can live in the community without need of residential care because their symptoms are controlled.